Liquefied gas and the like is transported in tankers in a liquid state. Thus the gas is cooled to a cryogenic temperature where its volatility is low and it is very easy to handle.
As a rule the chamber inside the tanker is subdivided by one or more partitions into a plurality of liquid-containing compartments. These separate compartments mainly serve to prevent the ship from sinking should the outer hull be pierced. Thus in case of accident only one of the compartments will be opened, only part of the cargo lost, and the tanker will remain afloat.
The partition walls are usually of a very heavy construction and provided with considerable insulation and heating equipment so as to protect these walls from the extreme low temperatures of the cryogenic liquids. Thus the walls frequently attain an overall thickness of 2.5 to 3 meters, and the space in the walls of the container approximately 0.5 meters. Thus in a tanker having four compartments, therefore having three coffer dams or partitions, the overall wall thickness is some 10 to 12 meters, equal to approximately 4.5% of the length of a tanker having an overall volume of 125,000 cbm. This type of construction raises the price of the tanker by approximately 3 million dollars.
In double-hulled ships such partitions are not needed for rigidifying the tanker, but are usually included only to protect against accidents as described above. Such ships are, however, extremely expensive to manufacture.